Changes in aboveground primary production and carbon and nitrogen pools accompanying woody plant encroachment in a temperate savanna

When woody plant abundance increases in grasslands and savannas, a phenomenon widely observed worldwide, there is considerable uncertainty as to whether aboveground net primary productivity (ANPP) and ecosystem carbon (C) and nitrogen (N) pools increase, decrease, or remain the same. We estimated ANPP and C and N pools in aboveground vegetation and surface soils on shallow clay and clay loam soils undergoing encroachment by Prosopis glandulosa in the Southern Great Plains of the United States. Aboveground Prosopis C and N mass increased linearly, and ANPP increased logarithmically, with stand age on clay loam soils; on shallow clays, Prosopis C and N mass and ANPP all increased linearly with stand age. We found no evidence of an asymptote in trajectories of C and N accumulation or ANPP on either soil type even following 68 years of stand development. Production and accumulation rates were lower on shallow clay sites relative to clay loam sites, suggesting strong edaphic control of C and N accumulation associated with woody plant encroachment. Response of herbaceous C mass to Prosopis stand development also differed between soil types. Herbaceous C declined with increasing aboveground Prosopis C on clay loams, but increased with increasing Prosopis C on shallow clays. Total ANPP (Prosopis+herbaceous) of sites with the highest Prosopis basal area were 1.2 × and 4.0 × greater than those with the lowest Prosopis basal area on clay loam and shallow clay soils, respectively. Prosopis ANPP more than offset declines in herbaceous ANPP on clay loams and added to increased herbaceous ANPP on shallow clays. Although aboveground C and N pools increased substantially with Prosopis stand development, we found no corresponding change in surface soil C and N pools (0–10 cm). Overall, our findings indicate that Prosopis stand development significantly increases ecosystem C and N storage/cycling, and the magnitude of these impacts varied with stand age, soil type and functional plant traits     

A juvenile plesiosaur (Plesiosauria: Reptilia) from the Lower Lias (Hettangian: Lower Jurassic) of Lyme Regis, England: a pliosauroid-plesiosauroid intermediate?

A partial skull and skeleton of a small, juvenile plesiosaur, part of the historically important Philpot Collection from Lyme Regis, England, is described. It is assigned tentatively to EwycMdus arcuatus (Owen, 1840) and has a mosaic of features which make it difficult to place in a superfamily. The characters of the posterior elements of the skull and post-dentary bones are close to those expected in a plesiosauroid, whereas the anterior dentition and symphysis of the lower jaw are more typical of a pliosauroid. The specimen is placed in the Pliosauroidea pending a phylogenetic revision of the Lower Jurassic Plesiosauria. From a reconstruction of the dentition and jaw-closing muscles, it is thought to have been a predator on soft-bodied or lighdy armoured prey, such as belemnoids, ammonites or small fish.     

Weighted finite population sampling to maximize entropy

Attention is drawn to a method of sampling a finite populationof N units with unequal probabilities and without replacement.The method was originally proposed by Stern & Cover (1989)as a model for lotteries. The method can be characterized asmaximizing entropy given coverage probabilities _i, or equivalentlyas having the probability of a selected sample proportionalto the product of a set of ‘weights’ w_i. We showthe essential uniqueness of the w_i given the _i. We present twomethods for stepwise selection of sampling units, and correspondingschemes for removal of units that can be used in connectionwith sample rotation. Inclusion probabilities of any order canbe written explicitly in closed form. Second-order inclusionprobabilities _ij satisfy the condition O < _ij < _ij, whichguarantees Yates & Grundy‘s variance estimator tobe unbiased, definable for all samples and always nonnegativefor any sample size.     

Analysis of Organ Specificity of a Low Temperature Responsive Gene Family in Rye (Secale cereale L.)

The barley (Hordeum vulgare L.) low temperature responsive geneblt14 was used as a probe, to isolate two different cognateclones (rlt1412; rlt1421) from a rye (Secale cereale L.) cDNAlibrary prepared from low temperature-treated (6°C day/2°C night) shoot meristems of the cultivar, Puma. Northernblot analysis revealed that low temperature expression of rlt1412is highest in root tissues whereas, rlt1421 shows greatest mRNAaccumulation in mature leaf tissues. There is a relationshipbetween the steady-state levels of these mRNA species and thefrost hardiness of Puma (North American cultivar) and Rhayader(UK cultivar) such that the expression ofboth genes is higherin the more frost hardy cultivar, Puma, compared with Rhayader. DNA and predicted amino acid sequence analysis indicated thatthe rye and barley clones encode small proteins with consensusN-terminal signal sequences whose biological function is atpresent unknown. The relevant sequences are lodged in the EMBL data base. Key words: Rye, cold, cDNA, organ specificity, low temperature genes     

Glutamine- and Asparagine-Dependent Protein Synthesis in Maturing Legume Cotyledons Cultured in vitro

Legume cotyledons have been grown in sterile culture and shownto synthesize up to 16 mg protein in 5 d when supplied witheither asparagine or glutamine as sole nitrogen sources. Glutamate,nitrate, and ureides also served as nitrogen sources for proteinsynthesis but to a lesser extent. Methionine sulphoximine and azaserine inhibited asparagine-dependentprotein synthesis suggesting that ammonia is liberated fromasparagine which is reassimilated via glutamine synthetase andglutamate synthase.     

Hormonal and host factors stimulating pheromone synthesis in female western pine beetles, Dendroctonus brevicomis

ABSTRACT. Newly-emerged, unfed Dendroctonus brevicomis females produced large quantities of the pheromone exo -brevicomin when treated topically with the synthetic juvenile hormone 10,11-epoxyfarnesenic acid methyl ester (JH III). No exogenous source of pheromone precursor was required, and decapitation experiments showed that the synthetic JH was effective in the apparent absence of brain hormone. However, implantations of combined corpora allata—corpora cardiaca from either newly-emerged or fed (i.e. pheromone producing) females failed to stimulate exo -brevicomin synthesis by recipient unfed beetles. Biosynthesis of exo -brevicomin was induced in newly-emerged females by ingestion of host phloem, and the stimulatory phloem component was found in methanol extracts. Neither less polar solvent extracts of phloem nor artificial distension of the gut with air was effective in stimulating pheromone synthesis.     

Where will species go? Incorporating new advances in climate modelling into projections of species distributions

Bioclimatic models are the primary tools for simulating the impact of climate change on species distributions. Part of the uncertainty in the output of these models results from uncertainty in projections of future climates. To account for this, studies often simulate species responses to climates predicted by more than one climate model and/or emission scenario. One area of uncertainty, however, has remained unexplored: internal climate model variability. By running a single climate model multiple times, but each time perturbing the initial state of the model slightly, different but equally valid realizations of climate will be produced. In this paper, we identify how ongoing improvements in climate models can be used to provide guidance for impacts studies. In doing so we provide the first assessment of the extent to which this internal climate model variability generates uncertainty in projections of future species distributions, compared with variability between climate models. We obtained data on 13 realizations from three climate models (three from CSIRO Mark2 v3.0, four from GISS AOM, and six from MIROC v3.2) for two time periods: current (1985–1995) and future (2025–2035). Initially, we compared the simulated values for each climate variable (P, T_max, T_min, and T_mean) for the current period to observed climate data. This showed that climates simulated by realizations from the same climate model were more similar to each other than to realizations from other models. However, when projected into the future, these realizations followed different trajectories and the values of climate variables differed considerably within and among climate models. These had pronounced effects on the projected distributions of nine Australian butterfly species when modelled using the BIOCLIM component of DIVA-GIS. Our results show that internal climate model variability can lead to substantial differences in the extent to which the future distributions of species are projected to change. These can be greater than differences resulting from between-climate model variability. Further, different conclusions regarding the vulnerability of species to climate change can be reached due to internal model variability. Clearly, several climate models, each represented by multiple realizations, are required if we are to adequately capture the range of uncertainty associated with projecting species distributions in the future.     

Phycobiliprotein fluorescence of Nostoc punctiforme changes during the life cycle and chromatic adaptation: characterization by spectral confocal laser scanning microscopy and spectral unmixing

Many cyanobacteria are highly adaptable to light quality, and many species undergo a complex life cycle. In this study we show that adaptive changes in the photosynthetic apparatus of cyanobacteria are not only caused by environmental, but also by developmental factors. Spectral confocal laser scanning microscopy (CLSM) was used to analyse in vivo the fluorescence spectra of the photosynthetic pigments chlorophyll a (Chl a), allophycocyanin (APC), phycocyanin (PC) and phycoerythrin (PE) of two Nostoc punctiforme strains. Changes in pigment fluorescence emission occurred in different developmental stages. Strain 1:1-26 showed an emission maximum at 674 nm in motile hormogonia stages, whereas vegetative stages showed maxima at 658 and 575 nm. These changes were not caused by chromatic adaptation. In contrast, the second strain (1:1-26lg) showed distinct fluorescence spectra, pigment localization and clear chromatic adaptation in red light. When these properties are known, both strains can be easily distinguished by the spectral CLSM method, which also allows the localization of the pigments within single cells. To calculate the contribution of individual phycobiliproteins to the observed changes, fluorescence spectra were analysed by spectral unmixing. This allowed the mathematical estimation of fluorescence shares for the individual phycobiliproteins in different developmental stages and both before and after chromatic adaptation. It is concluded that care should be taken when characterizing cyanobacteria by differences in pigment fluorescence, because these differences are influenced not only by chromatic adaptation, but also developmental stages. Spectral CLSM offers a powerful method to study the phycobiliprotein composition in vivo.